In a magnetically recorded data reproduction device, such as a magnetic card reader; an “F”&“2F” signal corresponding to a “0”&“1” datum is read out, the “F”&“2F” signal being magnetically-recorded, for example, by means of a frequency modulation method; and then the datum read out, which is frequency-modulated (by F2F modulation), is demodulated by a data demodulation device (demodulation circuit).
Proposed in Patent Document 1 is a demodulation method in which magnetic data recorded in a magnetic recording medium, such as a magnetic card, by means of a frequency modulation method is read out and the data is demodulated.
In the demodulation method described in Patent Document 1, a time period (a standard interval) as a result of multiplying an interval of an adjacent bit positioned one bit before a bit to be judged, by a certain rate (for example, 5/8), and an interval of the bit to be judged are compared each other in order to judge whether a datum of the bit to be judged is “0” or “1.”
[Patent Document]
Patent Document 1: Japanese Unexamined Patent Application Publication No. 58-50611*
In the method for demodulation described in Patent Document 1, one standard interval and an interval of a bit to be judged are compared each other in order to make a judgment on a datum of the bit. Therefore, in the case where a transfer speed of a magnetic recording medium fluctuates on a grand scale, or a recording accuracy of magnetic data recorded in a magnetic recording medium is low, unfortunately the magnetic data cannot be demodulated appropriately so that an error happens with a high possibility.